This invention relates to a cable burial tool used in a cable burial system of particular application to the burial of underwater cables in the sea floor.
A substantial portion of the world's transoceanic communications are carried on undersea cables buried in the sea floor. The cable normally includes lengths of signal carrier within a protective jacket, with intermediate amplifiers (termed "repeaters) located along the length of the cable in the case of a long cable. In the past, such cables were formed of copper electrical carriers, but today glass optical fiber cables are also widely used. Copper cables are usually 2-4 inches in diameter. Glass fiber cables are typically smaller in diameter than copper cables, often no more than 1/2 inch or smaller in diameter. In both cases, the repeaters are present as radial bulges in the cable which are located along its length.
Although the undersea cable may be laid on the top surface of the sea floor, for most applications it is preferred to bury the cable a foot or more below the sea floor. A cable lying on the surface of the sea floor is susceptible to damage due to adverse currents, marine fouling, fish bites, and fishing activities. Burying the cable in the sea floor avoids these types of potential damage to the cable.
A large number of techniques have been used over the years to bury cable in the sea floor. These techniques require the digging of a trench in the sea floor, feeding the cable into the trench, and closing the trench. The burial is accomplished at depths up to several thousand feet below the surface of the water. The cable burial techniques include the use of towed underwater vehicles such as sleds, remotely operated vehicles, and crawlers that crawl on the surface of the sea floor.
While operable, the available techniques all have limitations, particularly when the cable to be buried is a glass optical fiber cable. When the glass optical fiber is buried in the sea floor, provision must be made to pass the larger-diameter repeaters through the cable burial apparatus. There are typically limitations on the minimum bend radius and the maximum load which may be applied to the glass fiber optical cable, which are not met with existing cable burial apparatus. Existing cable burial systems also tend to be complex, which leads to concerns with system reliability. Further, considerations of economics mandate a cable burial apparatus that is operable at as high a linear travel rate as possible.
There is therefore a need for an improved cable burial system, particularly for use in burying optical fiber cables having periodic repeaters. The present invention fulfills this need, and further provides related advantages.